Highly Efficient Fe–N–C Electrocatalyst for Oxygen Reduction Derived from Core–Shell-Structured Fe(OH)₃@Zeolitic Imidazolate Framework

Fe–N–C electrocatalysts represent one of the most promising oxygen reduction catalysts to replace the expensive platinum (Pt)-based catalysts in fuel cells. Herein, we report a highly efficient zeolitic imidazolate framework (ZIF)-derived Fe–N–C electrocatalyst for the oxygen reduction reaction (ORR) in both alkaline and acidic solutions, which involves the formation of a core–shell-structured Fe(OH)3@ZIF-8. The encapsulated Fe(OH)3 in ZIF-8 gradually evolves into iron oxide with the increasing temperature during the carbonization, which plays several roles including creating Fe–Nx active sites, retaining morphology as a rigid template as well as tuning the carbon microstructure. The best-performing C–Fe(OH)3@ZIF-1000 catalyst features a hollow polyhedron (interior cavity: ca. 48 nm) with a thin carbon shell (ca. 5 nm), exhibiting a high Brunauer–Emmet–Teller (BET) surface area of 1021 m2 g–1. In alkaline solution, the ORR activity of C–Fe(OH)3@ZIF-1000 surpasses the benchmark Pt/C catalyst, with the onset potential (Eonset) of 0.99 V (vs RHE) and the half-wave potential (E1/2) of 0.88 V (vs RHE). In acidic solution, the difference in E1/2 between C–Fe(OH)3@ZIF-1000 and Pt/C is 60 mV (0.80 vs 0.86 V), ranking it among the best Fe–N–C electrocatalysts in acidic media. The H2–O2 proton exchange membrane fuel cell (PEMFC) with C–Fe(OH)3@ ZIF-1000 as the cathode catalyst delivers a maximum power density of 411 mW cm–2 at 0.35 V.